The present invention relates to a drive unit for a wheel of an airplane landing gear.
Conventionally, the wheel unit of an airplane is a simple unit in which a friction brake having many disks was attached to the inside of a tire wheel and does not have a strong drive unit to control the running speed of the airplane at the time of takeoff and landing.
Consequently, the running distance at the time of takeoff can not be shortened by the wheel unit and the wheel can not be turned at a high speed in synchronization with landing speed.
Furthermore, the conventional brake unit, when used to reduce speed immediately after landing, generates a large amount of heat by friction between the brake disks and, therefore, many transport airplanes let down the flaps provided at the rear periphery of the main wings and then use the reverse thrust of the jet engines to reduce speed. Further, and the wheel brake can be used only after the speed is greatly reduced by the air resistance of the flap, thus necessitating a long running distance.
Normally, on take off an airplane having fixed wings, supported by a landing gear, utilizes the thrust force of the engine; however, it requires a long runway to reach takeoff speed.
At the time of landing, the airplane descends by gradually reducing engine power and then lands on the runway using the landing gear. At this time, the stationary tire touches the runway with a great impact, and generates white smoke, when beginning to turn, due to the shock of landing causing heat adhesion to the runway and also damage to itself.
Airplanes, which are the fastest means of transportation, to meet with the growing demand for international transportation in shorter times, are being designed in larger sizes for long-distance flights and a larger airplane needs a longer runway, consumes a larger volume of fuel, and generates more noise in the vicinity of the airport.
The present invention solves the foregoing problems by providing a compact, high-torque, high-speed drive unit/pneumatic actuator for the wheel unit of an airplane landing gear to secure safety at the time of takeoff and landing. At the time of taking off, the drive unit/pneumatic actuator of the present invention accelerates the airplane with a strong torque and, at the time of landing, reduces the shock to the tire by turning the wheel at a high speed equal to or approaching landing speed prior to landing, and functions as a vacuum brake by reducing the speed of the airplane immediately after landing.
The pneumatic actuator (motor) of the present invention uses a (first) impeller, operating as an expander, which is driven at a high speed by the velocity of the compressed air as a primary force (velocity energy) and uses a turbine-type impeller which is driven by the air exhausted from the first impeller and undergoing expansion (pressure or expansion energy), and thus transmits a powerful torque and high-speed rotation to the wheel. In this way it serves a constant-velocity, high-performance pneumatic motor.
The pneumatic actuator configured as described above is a pneumatic motor having a series of drive impellers by which a large volume of compressed air is fed, via the first impeller, to an expansion chamber within the casing, wherein it is expanded. The expanding air then passes through the second impeller. This pneumatic motor/actuator has an impeller rotational speed that is inversely proportional to the decrease of load resistance of the wheel and to the energy of the compressed air fed thereto. The synergy of the above two phenomena results in continuous acceleration of the wheel with no reduction in the torque of the impeller as the rotational speed of the wheel increases.
Furthermore, the present invention provides (1) a drive unit which drives the wheel with an ultra-high rotary speed that can match the speed of the airplane upon landing, and a strong drive force which assists the airplane to run on the runway at high speed upon takeoff and (2) a compact, continuous-velocity wheel unit which takes only a short time from start-up to reach its maximum power.
In the present invention, in order to realize the above features, vanes of the first impeller are fixed within a speed ring in the form of a three-sided, annular enclosure and the turbine-type vanes of the second impeller are fixed to an interior cylindrical surface of the speed ring and extend radially inward thereof. Thus, in the preferred embodiment, the first and second impellers are integrated with the speed ring into a single, integral (xe2x80x9cdouble turbinexe2x80x9d) unit, whereby the first and second impellers are fixed together and rotate together. The speed ring is mounted in a round housing formed in the periphery of the casing and providing an airtight covering so that the compressed air introduced into the side of the round housing flows through and drive the first impeller, then enters the expansion chamber, which is open on one side to the second impeller fixed to the interior of the speed ring, and then passes through the second impeller. The inner ends of the vanes of the second impeller are fixed to the wheel axle, whereby the turning of the speed ring with the first and second impellers drives the wheel.
Furthermore, a fan-blade-type third impeller having a plurality of long, thin vanes is mounted on and fixed to the wheel axle, within an exhaust opening of the casing, so that compressed air which is exhausted at a high velocity may be discharged smoothly to the outside, and the wheel is attached to the flange of the impeller so that they turn together.
Furthermore, a fixed vane is mounted between and coaxial with the second and third impellers so that air flow therebetween is straightened and vibration of the impellers is suppressed.
One advantage of the actuator of the present invention is that there is no upper limit on its rotary speed. In contrast, electric motors and internal combustion engines, for example, have a maximum speed of revolution due to load resistance and, hence, are inappropriate for the landing gear of an airplane.